Heat developable paper



p 1954 M. F. BAUMANN ETAL 3,149,991

HEAT DEVELOPABLE PAPER Filed Jan. 5, 1962 CO-CRYSTAL ADDUCT OF AN AMINE AND A BISPHENOL Q A KETO COMPOUND (AMINE AND KETO COMPOUND BEING DYE PRECURSORS.)

SUPPORT INVENTORS MICHAEL F. BAUMANN BY WILLIAM R.LAWTON ATTORNEYS United States Patent 3,149,991 HEAT DEVELGPABLE PAPER Michael F. Haurnann, Hudson, and William R. Lawton, Nashua, N.H., assignors to Nashua Corporation, Nashua, N.H., a corporation of Delaware Filed 5, 1962, Ser. No. 164,594 6 Claims. (Ci. 117-363) This invention relates to heat marking processes and provides a novel heat sensitive sheet useful for copying and recording uses, and characterized by the ability to form a mark of contrasting color when heated to an activation temperature in the range of 50 to 150 C. Sheets of this type are commonly employed in thermographic copying processes, in which a sheet is placed next to a graphic original and is exposed with the original to infrared radiation which causes selective heating of the dark areas of the original suflicient to form a copy thereof on the copy sheet. A more detailed description of this process is set forth in US. Patent No. 2,740,896. The sheets of this invention may also be used in recording devices in which marking is accomplished by means of a heated stylus.

In the heat marking sheets of this invention, materials which are reactive to form a dye are incorporated in the sheet in intimate association. These materials, referred to herein as precursors of the dye, include an organic keto compound, that is a ketone or aldehyde, and a primary or secondary amine. Numerous well known dyes are formed from precursor materials of this type; those useful in this invention are those which will react to form a dye when mixed together at temperatures below 150 C.

In the heat marking sheets of this invention, both precursors are present in the sheet, with the amine being present as a component of a solid stable co-crystal adduct formed by combining the amine with a bisphenol. Adducts of this type are described in US. Patent No. 2,829, 175, and also in the co-pending application of William R. Lawton and Eugene F. Lopez, Serial No. 840,514, filed September 17, 1959, now US. Patent No. 3,104,979, assigned to the assignee of this application.

The organic keto compound should be lightly colored solid and non-hygroscopic, and otherwise stable at normal conditions of temperature and humidity, that is, those conditions one might expect to encounter in actual conditions of storage, shipment, and use.

Several classes of keto compounds have been found to be effective in compositions of the present invention. Representative of these compounds and particularly useful are the ketones and aldehydes of monoand polynuclear aromatic compounds, and quinoid compounds.

The cocrystal adduct should be similarly stable, and lightly colored, and should in addition be dissociable to yield the amine component at the desired activation tem perature in the range of 50-150 C. The particular amine and bisphenol are accordingly to be selected with reference to these criteria on the basis of known, or readily ascertainable, characteristics of the materials of this type.

In typical representative embodiments of this invention, the keto compound and the co-crystal adduct are dispersed separately or together in a binder solution and applied as one or more coatings to a paper or other base by conventional techniques. The keto compound may be dissolved in the binder solution, but if so, the solvent should not be one that attacks the co-crystal adduct to bring about premature color reaction. The relative proportions of the two components should be such as to provide mutual reaction, with a total concentration sufficient to produce a distinct contrasting color mark when the sheet is heated. These quantities are generally not critical and may be determined by routine experimentation.

The following examples describe in detail several representative embodiments of this invention.

Example 1 A co-crystal adduct is first formed by combining:

Grams Tetrachlorobisphenol A (TCBA) 183 Ethyl ethanol amine 89 Toluene 550 Parts by weight TCBA/EEA 1O Polyvinyl butyral (Butvar B-76) 2.5 Trichloroethylene 87 The mixture is charged in a ball mill and milled overnight at 40 F.

A second dispersion is prepared consisting of:

Parts 2,S-dichloronaphthoquinone 10 Polyvinyl butyral (Butvar B-76) 2.5 Trichloroethylene 87.5

This mixture is similarly charged in a ball mill and milled overnight at 40 F.

The two dispersions are now mixed in the ratios of 11.0 parts of the TCBA/EEA dispersion to 13.5 parts of the 2,S-dichloronaphthoquinone dispersion, and the resulting mixture is coated on a 25-pound per ream (500 sheets, 24 inches by 36 inches) glassine at a dry-coating weight of 4.0 pounds per ream. The resulting coated sheet provides satisfactory reproductions when employed as a thermographic copy in a Minnesota Mining and Manufacturing Company Thermo-Fax Secretary Model 17H copying machine on the range of the machine settings of 1-7.

Satisfactory copy sheets may be formed in the manner described in Example 1 by substituting for the 2,5-dichloronaphthoquinone, in comparable molar ratios with the amine of the co-crystal adduct, ketone derivatives of related aromatic and quinoid compounds, such as 1,4- naphthoquinone; Z-amino-1,4-naphthoquinone; tetrachlorobenzoquinone; Z-methyl-1,4-naphthoquinone; l-nitroanthraquinone; 1,5-dinitroanthraquinone; l-nitro, 2-carboxy-anthraquinone; 9,10-dihydro-9-oxyanthracene.

Further satisfactory copy sheets may be prepared by substituting for the TCBA/EEA of Example 1 a co-crystal adduct of any primary or secondary amine selected from the class consisting of hydrazine, alkyl amines, cycloalkyl amines, aryl amines, alkanol amines, aralkyl amines and heterocyclic amines. Examples of some of these amines which have been employed in the preparation of satisfactory embodiments of the present invention are hydrazine, hexylamine, dibutylamine, cyclohexylamine, dicyclohexylamine, ethanol, diethanol, polyglycolamine, phenylethanolamine, analine, N-aminomethylpiperazine, aminoethylethanolamine, ethylcyclohexylarnine, morpholine, piperidine.

Example 2 In a preferred embodiment of the present invention the keto compound is selected from the group of aromatic ketones bearing the typical polynuclear indane structure,

specifically indane-1,2,3-trione-2-hydrate. The selected keto compound and the co-crystal adduct formed from tetrachlorobisphenol A and hexanediamine are applied to the carrier sheet as dispersions in successive coating layers.

The composition in the first layer consists of:

7 Parts Trichloroethylene 84 Indane-1,2,3-trione-2-hydrate (Ninhydrin) 8 Binder, Formvar 7/70 8 amine in the manner described in Example 1 15 Binder, Staybelite No. 10 (glyceryl ester of hydrogenated resin) 1O Hexane 40 The binder is first dissolved in the hexane, and the cocrystals are then added and dispersed by ball milling for 24 hours. The dispersion is applied over the first coat at the rate of about 3 pounds per ream.

When dried, the sheet is very well suited for conventional thermographic copy processes.

Additional copy sheets may be prepared in the manner described in Example 2 by employing other indane ketones such as indane-1,2,3-trione; indarie-LZ-dione; indane-1,3- dione; bis-indane-1,3-dione; Z-hydroxy-indane-1,3-dione; bis-2-hydroxy-indane-1,3-dione; 2-phenyl-indane-1,3-dione. As previously suggested with reference to Example 1, further practical copy sheets may be prepared by substituting various co-crystal adducts of primary and secondary amines for that specified in Example 2.

It will be observed in Example 2 that the resin binder of the first layer is insoluble in the solvent of the second layer, and that thereby two distinct layers are formed without intermingling. Best results are obtained from two incompatible resins in this manner, but satisfactory results can be obtained when compatible resins, or the same resin, are employed in both layers.

Example 3 Various aromatic aldehydes may be employed as the keto compound in the preparation of copy sheets of the present invention. The following is a typical example.

A base sheet as previously described is coated with a 10% solution of 2,4-dinitrobenzaldehyde in ethyl alcohol at a rate sufficient to deposit about 1-2 pounds per ream of the aldehyde. When dried this layer is topcoated to about 3 pounds per ream from a dispersion consisting of:

Parts Tetrachlorobisphenol A/diethanolamine co-crystals, prepared from tetrachlorobisphenol A and the amine in the manner described in Example 1 15 Pliolite VT (vinyl toluene/butadiene resin) 10 VM & P Naphtha 50 The previously noted substitutions of various co-crystal adducts may be employed with respect to Example 3 as well and, in addition, other keto compounds may be used, such as 3,S-dinitrosalicylaldehyde; 3,5-dichlorosalicylaldehyde; 5-chl0rosalicylaldehyde; o-nitrocinnamaldehyde; 5-chlorovanillin; S-nitrovanillin; 5-'nitrosalicylaldehyde.

The sheets described in the foregoing examples have activation temperatures in the range of 50 C. to 150 C., as determined by placing the sheet against a heated surface for 1 second, and measuring the lowest temperature at which a visibly distinct color change occurs in the heated area.

The accompanying drawing illustrates schematically a heat-sensitive sheet corresponding to this invention. The sheet is represented as being in cross-section.

Although this invention has been described with reference to representative and preferred embodiments, it is contemplated that obvious modifications will occur to those skilled in the art and familiar with these teachings, and that such may be made without departing from the scope of this invention. Other color forming systems based on keto compounds and primary or secondary amines are known in the art and many of them will undoubtedly be found to be useful in this invention. Other bisphenol compounds, such as those described in the above-identified co-pending application of Lawton and Lopez may be also used with suitable amines, provided that selection is made on the basis of the criteria set forth herein. Other binder materials may be employed, such as chlorinated rubber, polyvinyl acetal, acrylic ester polymer, polyvinyl acetate, polyvinyl ethyl ether, polyvinyl methylol resin. Other ingredients may also be included in the coating such as anti-tack agents, anti-finger printing agents, and anti-static agents, and bases other than glassine, e.g. regenerated cellulose, cellulose esters, other forms of paper and plastic materials may also be used if desired.

Having thus disclosed our invention and described in detail preferred embodiments thereof, we claim and desire to secure by Letters Patent:

1. A heat sensitive sheet adapted for dry heat marking processe, stable and lightly colored under normal conditions and responsive to heating to an activation temperature in the range of 50 C. C. by changing visibly and irreversibly to a contrasting color through the formation of a dye, said sheet including a solid stable lightly colored non-hygroscopic keto compound selected from the group consisting of ketones and aldehydes of monoand polynuclear aromatic compounds and quinoid compounds, and a solid stable crystalline co-crystal adduct of a bisphenol and an amine selected from the group consisting of primary and secondary amines and hydrazine, said amine and keto compound being dye precursors which when combined are reactive at a temperature of less than 150 C. to form said dye, said adduct having a dissociation temperature between 5 0 C. and 150 C. at which said amine is released for reaction with said keto compound.

2. A heat sensitive sheet adapted for dry heat marking processes, stable and lightly colored under normal conditions and responsive to heating to an activation temperature in the range of 50 C.150 C. by changing visibly and irreversibly to a contrasting color through the formation of a dye, said sheet including a solid stable lightly colored non-hygroscopic keto compound selected from the group consisting of ketones and aldehydes of monoand poly-nuclear aromatic compounds, and quinoid compounds, and a solid stable crystalline co-crystal adduct of a bisphenol and an amine, said amine and keto compound being dye precursors which when combined are reactive at a temperature of less than 150 C. to form said dye, said adduct having a dissociation temperature between 50 C. and 150 C. at which said amine is released for reaction with said keto compound, said keto compound and said adduct each being dispersed as intimately associated particles in a binder resin, and forming therewith a heat sensitive coating on said sheet.

3. A heat sensitive sheet adapted for dry heat marking processes, stable and lightly colored under normal conditions and responsive to heating to an activation temperature in the range of 50 C.150 C. by changing visibly and irreversibly to a contrasting color through the formation of a dye, said sheet including a solid stable lightly colored non-hygroscopic keto compound selected from the group consisting of ketones and aldehydes of monoand poly-nuclear aromatic compounds, and quinoid compounds, and a solid stable crystalline cocrystal adduct of a bisphenol and an amine, said amine and keto compound being dye precursors which when combined are reactive at a temperture of less than 150 C. to form said dye, said adduct having a dissociation temperature between 50 C. and 150 C. at which said amine is released for reaction with said keto compound, said keto compound being dispersed in a binder resin and forming therewith a first layer, and said adduct being dispersed in a binder resin and forming therewith a second layer adjacent to said first layer.

4. The sheet as defined by claim 1, wherein the keto compound is a quinone.

5. The sheet as defined by claim 1, wherein the keto is a polyketone indane derivative.

6 6. The sheet as defined by claim 1, wherein the keto compound is an aromatic aldehyde.

References Cited in the file of this patent UNITED STATES PATENTS 2,663,656 Miller et al. Dec. 22, 1953 2,899,334 Crevling et a1 Aug. 11, 1959 2,967,785 Allen et al. Ian. 10, 1961 2,995,466 Sorensen Aug. 8, 1961 3,024,362 Sus et a1. Mar. 6, 1962 3,076,707 Lawton et al. Feb. 5, 1963 

1. A HEAT SENSITIVE SHEET ADAPTED FOR DRY HEAT MARKING PROCESSES, STABLE AND LIGHTLY COLORED UNDER NORMAL CONDITIONS AND RESPONSIVE TO HEATING TO AN ACTIVATION TEMPERATURE IN THE RANGE OF 50*C.-150*C. BY CHANGING VISIBLY AND IRREVERSIBLY TO A CONTRASTING COLOR THROUGH THE FORMATION OF A DYE, SAID SHEET INCLUDING A SOLID STABLE LIGHTLY COLORED NON-HYDROSCOPIC KETO COMPOUND SELECTED FROM THE GROUP CONSISTING OF KETONES AND ALDEHYDES OF MONO- AND POLYNUCLEAR AROMATIC COMPOUNDS AND QUINOID COMPOUNDS, AND A SOLID STABLE CRYSTALLINE CO-CRYSTAL ADDUCT OF A BISPHENOL AND AN AMINE SELECTED FROM THE GROUP CONSISTING OF PRIMARY AND AN AMINE SELECTED FROM THE GROUP CONSISTING OF PRIMARY AND SECONDARY AMINES AND HYDRAZINE, SAID AMINE AND KETO COMPOUND BEING DYE PRECURSORS WHICH WHEN COMBINED ARE REACTIVE AT A TEMPERATURE OF LESS THAN 150*C. TO FORM SAID DYE, SAID ADDUCT HAVING A DISSOCIATION TEMPERATURES BETWEEN 50*C. AND 150*C. AT WHICH SAID AMINE IS RELEASED FOR REACTION WITH SAID KETO COMPOUND. 